1. Field of the Invention
The present invention relates to a method and system or apparatus for non-invasively adjusting the position of at least one implanted electrode.
2. Description of the Prior Art
Heretofore, leads designed for electrical stimulation of human tissue generally comprise electrodes at their distal end which are connected to contacts at their proximal end via insulated conductor wires threaded inside a non-conductive sheath. In general, stimulation leads are used to transport electrical pulses from an implanted pulse generator to the target tissue.
In the case of spinal cord stimulation, the target tissue is a secluded nerve fiber(s) within the spinal cord which transport a distinct neurological message to or from the brain. Two examples of a neurological message are (1) a signal to the brain intended to trigger a defensive or protective action, such as pain or (2) a signal from the brain intended to contract a specific muscle, such as the urinary bladder sphincter.
In the first example, electrical stimulation can be used to modify the pain signal in order to induce analgesia by activation of the endogenous opiate pain suppression system in a specific part of the body.
In the second example, electrical stimulation can be used to cause the contraction of the sphincter in the urinary bladder in order to prevent urinary incontinence.
Trying to recruit specific nerve fibers without affecting other nerve fibers can be a very difficult and time consuming medical procedure. When using electrical stimulation for pain control, a trial stimulation is applied to the spinal cord using an external pulse generator, with the goal of positioning the electrode so that a fine, tingling sensation called paresthesia, is felt in the entire area where there is pain. During this trial stimulation, a patient needs to be fully awake in order to report to the physician when optimal localization of the electrode has taken place. Once the optimal electrode position is achieved, the lead is sutured in place, disconnected from the external pulse generator and connected to an implantable, permanent pulse generator which is then programmed to the same stimulation values as the external one.
Some types of neural stimulation are notoriously ineffective, such as lower back stimulation. The spacing between electrodes and the length of each electrode become very critical factors for effective lower back stimulation. For some patients the physician may choose a lead having large spacing between electrodes in order to achieve complete paresthesia coverage, only to find out that such large spacing makes it too difficult if not impossible to recruit the target nerve. A lead having closely spaced electrodes may facilitate recruitment of the target nerve but may not provide complete paresthesia coverage. The main problem here is that manual pushing or pulling of the implanted lead by the physician often results in larger than desired changes in electrode position, making location of the "sweet spot" (parasthesia location) extremely difficult. An electromechanical means for micro-stepping (rotating) the electrode position, such as described hereinafter, will allow the physician to locate the desired location quicker and with less effort, improving the chances for successful therapy.
Furthermore, one of the major obstacles in preventing long term success of spinal cord stimulation for some patients, has been electrode displacement from their originally implanted position relative to the target nerve. Electrode displacement in most cases is due to normal flexing of the spinal column as the patient goes about his/her normal daily activities. What appears to occur is that the lead retracts slightly when the patient bends forward, but does not fully recoil back to its original location upon the patient returning to the up-right position. This results in a decreased or total loss of medical therapy. In this case, if the system of the present invention is used and the patient is provided with an electrode position controller, a physician or a properly trained patient may be able to non-invasively reposition the electrode to the original site and avert an expensive and uncomfortable surgical procedure to manually reposition the electrode.